The Bird in the Waterfall by Jerry Dennis and Glenn Wolff

Storm Surge
Jerry Dennis & Glenn Wolff

When coastal regions are struck by great ocean storms, most of the destruction is caused, not by wind, but water pushed ahead of the storm like snow before a shovel. When this shoved water, or storm surge, reaches shore it is often called a "storm tide" or "tidal wave," though it has no more connection with gravitational tide than does a tsunami.

The strong winds of tropical cyclones -- known variously around the world as hurricanes, typhoons, or cyclones -- create waves driven so relentlessly forward that they begin to crowd upon one another, piling up when they reach shallow water and creating a continuous current rushing landward faster than it can return to the sea. Hurricanes with winds of 75 to 95 miles per hour will typically produce a storm surge about five feet high, while winds of 130 to 155 miles per hour can be preceded by a storm surge as high as 18 feet. All that water surging over the land becomes a foundation for waves, which in turn cause more flooding. Such flooding can extend miles inland.

Storm surges are enhanced by the extremely low atmospheric pressure that accompanies tropical cyclones. The low pressure at the center of the storm causes the water beneath it to rise in a "hump" that floods inland as the storm strikes a coast.

The Galveston, Texas, hurricane of 1900 is an example of how destructive the combination of storm surge and large waves can be. That storm brought winds of 120 miles per hour and a storm surge 15 feet higher than the usual high tide. The surge carried 25-foot waves into Galveston, leveling much of the city and drowning 5,000 people. Even more terrible was the 30-foot storm surge that swept inland along the Bay of Bengal in November 1970, killing an estimated 200,000 to 300,000 people in Bangladesh.

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